The present invention relates to in-situ mining of metals such as copper and, more particularly, to a gas sparging method and apparatus for introducing fine bubbles of gas into the lixiviant or leaching liquor, used in such mining processes. The invention can be employed to a great advantage in situations where a gaseous oxidant is required to solubilize metal values.
The recovery of copper and other metals by conventional procedures, such as open pit mining and underground tunneling, has in recent years, become more costly and time consuming. For these reasons, and also because of the increasing demand for copper, other methods of copper recovery have been sought. As a result, it is now feasible to recover copper, even at great depths, by various in-situ mining techniques.
In such in-situ mining operations, a well is drilled to the level of the recoverable metal values. A liquid lixiviant, such as for example, ammonia-ammonium sulfate or ferric sulphate is then supplied through the well bore to the ore formation wherein it reacts with the metal values in the ore formation to produce a pregnant liquor containing the metal values therein. This pregnant liquor is then withdrawn from the ore formation through the same well bore, or through a series of closely spaced bores surrounding a central well bore, by pumping, or through a gas lift operation. A variety of such in-situ mining techniques are known in the art.
In many in-situ mining techniques it is advantageous to introduce a gas, such as oxygen, into the lixiviant supplied to the well bore. In many systems, a gas cooperates with the lixiviant to improve the leaching of the metal values from the ore formation. Usually an oxidizing gas such as air, oxygen, or air enriched with oxygen is used. This gas may also be supplemented with a catalyst such as SO.sub.2, or an acid forming gas such as SO.sub.3. An important example of a system in which a lixiviant containing bubbles of gas is used to leach metals is the so called "oxygen-water" system.
It has been found that the size of the gas bubbles introduced into the lixiviant will aid in the removal of metal values from the ore formation; and, it is desirable to supply the gas in the form of a large quantity of extremely fine or small diameter bubbles.
Accordingly, it is an object of the present invention to provide a method and apparatus for supplying fine bubbles to a lixiviant solution which is to be used in in-situ mining operations.
Another object of the present invention is to provide an apparatus for forming fine bubbles in a lixiviant solution which is relatively simple and inexpensive in construction.
Yet another object of the present invention is to provide a process for in-situ mining of minerals containing metal values such as copper values, by supplying a lixiviant to a plurality of sintered powdered metal porous tubes and supplying a gas to the exterior of these tubes, under pressure, so that the gas penetrates into the interior of the tubes and is wiped therefrom as fine bubbles by the lixiviant passing through the tubes.
Yet another object of the present invention is to provide an apparatus for introducing finely divided gas bubbles into a lixiviant used for in-situ mining of minerals which includes a hollow casing having first and second separate chambers formed therein with the lixiviant being supplied to the first chamber and gas under pressure supplied to the second chamber which also contains a plurality of porous tubes formed of sintered powdered metal, each having one end in communication with the first chamber so that the lixiviant flows through the tubes while gas penetrates into the tubes to form fine bubbles which are wiped from the tubes by the lixiviant and intermixed therewith.